The invention concerns additive compositions and lubricating compositions containing the described additive compositions which have improved antioxidant effects. These antioxidant additive compositions, when added to a base oil to form a lubricating composition, result in low levels of deposits and display improved copper corrosion inhibition and friction properties
It is known from the prior art that certain organomolybdenum complexes possess desirable lubricating characteristics including antiwear or antioxidant properties.
U.S. Pat. No. 5,364,545, assigned to Tonen Corporation, which is hereby incorporated by reference, describes a lubricating oil composition having a low coefficient of friction and reduced copper corrosion as a 3 component system comprising: (a) a lubricating oil basestock, (b) from 0.01 to 10% by weight, based on the oil composition, of at least one organomolybdenum compound selected from the group consisting of oxymolybdenum monoglyceride and oxymolybdenum diethanolamide; and (c) from 0.5 to 7% by weight, based on the oil composition, of at least one organozinc compound selected from the group consisting of zinc dithiophosphate (ZnDTP) and zinc dithiocarbamate.
The invention of Tonen Corp. is directed toward compositions which include a ZnDTP as can be seen from their described examples. Components such as ZnDTP act as antiwear, metal passivator and antioxidant agents in lubrication formulations. However, use of these metal phosphate compounds often result in poisoning of the catalytic converter and as such the need remains for an additive composition which does not require a metal phosphate compound.
U.S. Pat. No. 5,840,672, assigned to Ethyl Corporation, which is hereby incorporated by reference describes an antioxidant system for lubrication base oils as a 3 component system comprising MOLYVAN(copyright) 855 (organomolybdenum complex of organic amide)/ADPA(alkylated diphenylamine)/sulfurized isobutylene and/or sulfurized phenol. This invention relates to antioxidant compositions comprising (A) at least one secondary diarylamine, (B) at least one sulfurized olefin and/or sulfurized hindered phenol, and (C) at least one oil soluble molybdenum compound.
However, it is well known in the art that while it is possible to have a good antioxidant system in the additive composition, the resulting lubricating composition after the additive composition has been added can result in unacceptable levels of deposits or sludge when exposed to high temperatures such as those temperatures observed during operation of an engine.
U.S. Pat. Nos. 6,017,858 and 6,369,005, both assigned to R. T. Vanderbilt Company, Inc., which are hereby incorporated by reference, describes synergistic organomolybdenum compositions and lubricating compositions based on 2 component synergistic system: (1) MOLYVAN(copyright) 855 lubricant additive and (2) 1,3,4-thiadiazole compounds or DTC (dithiocarbamates) or DTP (phospborodithioate) compounds. This invention relates to synergistic antiwear compositions comprising an organomolybdenum complex and an organic sulfur compound selected from 2,5-dimercapto-1,3,4-thiadiazole derivatives, bisdithiocarbamate esters, metal dithiocarbamates, metal phosphorodithioates and phosphorodithioate esters. The organomolybdenum complex is a reaction product prepared by reacting 1 mole fatty oil, 1.0 to 2.5 moles diethanolamine and a molybdenum source.
Surprisingly, it has been discovered that an additive compositions which comprises (1) an organomolybdenum compound; (2) an alkylated diphenylamine; and (3) a sulfur containing compound selected from the group consisting of: (a) thiadiazole; (b) dithiocarbamate; and (c) mixtures of (a) and (b) unexpectedly possess antioxidant properties. In addition, the additive compositions of the invention also result in low levels of deposits and possess improved copper corrosion inhibition and friction properties when added to a base oil to form a lubricating composition.
According to the invention, there are provided improved antioxidant additive compositions comprising:
(1) an organomolybdenum compound;
(2) an alkylated diphenylamine; and
(3) a sulfur containing compound selected from the group consisting of:
(a) thiadiazole;
(b) dithiocarbamate; and
(c) mixtures of (a) and (b)
Also provided are lubricating compositions which contain the improved antioxidant additive compositions described above.
The antioxidant additive compositions of the invention, when added to a base oil to form a lubricating composition, result in low levels of deposits and display improved copper corrosion inhibition and friction properties.